Method for manufacturing a shock absorber reservoir tube

ABSTRACT

In preferred form, a method of manufacturing a shock absorber tube from sheet metal comprising the steps of forming a tube section having a longitudinal seam weld along the length thereof; forming a concave die having an inside surface with a central opening therein and a plurality of radial grooves extending from the central opening to the outer peripheral edge of the concave surface; pressing the tube into the die and causing the metal at one end of the tube to form into the inside surface of the concave die to cover ribs between the grooves and to flow into the grooves so as to form spaced, inwardly and outwardly directed reinforcing ribs and a small diameter tapered opening through the formed tube surrounded by a high-density concentration of material; thereafter locating a connector element against the high-density concentration of material and heating and pressing the metal to cause it to flow into the tapered opening for sealing the end of the tube while sinking the connector into the end of the tube for connection to the spaced reinforcing ribs.

United States Patent Gerstle Feb. 22,1972

[54] METHOD FOR MANUFACTURING A SHOCK ABSORBER RESERVOIR TUBE De Witt F. Gerstle, Dayton, Ohio General Mich.

[22] Filed: June 29,1970

[2|] Appl.No.: 50,529

[72] Inventor:

[73] Assignee: Motors Corporation, Detroit,

[56] References Cited UNITED STATES PATENTS 2/1957 Bailey ..29/475X 5/1966 Boteler ..29/475X Primary Examiner-John F Campbell Assistant Examiner-Richard Bernard Lazarus Attorney-W. S. Pettigrew and .l. C. Evans 5 7] ABSTRACT In preferred form, a method of manufacturing a shock absorber tube from sheet metal comprising the steps of forming a tube section having a longitudinal seam weld along the length thereof; forming a concave die having an inside surface with a central opening therein and a plurality of radial grooves extending from the central opening to the outer peripheral edge of the concave surface; pressing the tube into the die and causing the metal at one end of the tube to form into the inside sur face of the concave die to cover ribs between the grooves and to flow into the grooves so as to form spaced, inwardly and outwardly directed reinforcing ribs and a small diameter tapered opening through the formed tube surrounded by a high-density concentration of material; thereafter locating a connector element against the high-density concentration of material and heating and pressing the metal to cause it to flow into the tapered opening for sealing the end of the tube while sinking the connector into the end of the tube for connection to the spaced reinforcing ribs.

4 Claims, l4 Drawing Figures PATENTEDFEB 22 m2 SHEET 2 BF 3 ATTORNEY PAIENTEmzazz m2 3. 643.322

saw 3 or a INVEN'IOR ATTORNEY METHOD FOR MANUFACTURING A SHOCK ABSORBER RESERVOIR TUBE This invention relates to shock absorbers for automobiles and more particularly to an improved method for forming an integral cup on one end of steel tubing that defines the reservoir tube of adouble direct acting hydraulic chock absorber.

In many present day shock absorber reservoir tubes made of sheet metal there is a separate base cup on the bottom end of the reservoir tube that is connected to the reservoir tube by a continuous circumferential weld joint.

Such separate cups require a male and female die combination to define'a plurality of separate raised surfaces within the cup for supporting a base valve assembly used in shock absorbets having such reservoirs.

In order to have adequate strength the separate base cup of such unis is made from a relatively heavy gauge material. Furthermore, it requires a separate joining operation to sealingiy connect the reservoir tube to the periphery of the cup.

An object of the present invention is to simplify the manufacture of a shock absorber reservoir tube with an integral end cup by a methodthat forms it from a single metal blank by use of a ainglefernale die including a concave surface configuration thereon for forming an opened end of a sheet metal tube radially inwardly and on .itself to form a small diameter tapered opening at the end of the tube surrounded by a high concentration of sheet metal material defining a plurality of easily heated sharp edges; and thereafter locating a connector element on the outer surface of the tube at the tapered opening therethrough and applying a resistance welding current across the tube and the connector element to heat the high concentration of metal to cause it to flow into the tapered opening for filling the tapered opening with is melted metal plug; and simultaneously pressing the connector element into the end of the tube so as to securely connect it in place thereon.

Still another object of the present invention is to provide an improved method for forming a shock absorber reservoir tube with an integral end cup form sheet material comprising the steps of: rolling a strip of steel into a tube having a pair of longitudinal edge portions thereon. seam welding the longitudinal edges together to form a sealed joint along the length of the tube. locating the seam welded tube in axial alignment with a concave die surface having a central opening therein and a plurality of radial grooves extending from the opening to the peripheral edge of the concave surface at cquidistantly spaced circumferential locations and wherein each of the grooves is separated by a raised rib; pressing one end of the tube into the concave surface to cause the tube to be forced radially inwardly of itself into a cup shape by metal forming across the ribs and-into the grooves to form reinforcing ribs and to be pressed in the direction of the opening through the die into a tapered opening defined by a plurality of circumferential metal folds or crimped material forming high density concentralion of metal completely around the tapered opening; thereafter coining the end of the tube to form a controlled diameter opening to the inside of the tube; locating a connector element on the outside surface of the tube at the tapered opening therein and applying heat and pressure so as to cause the high density metal to melt into the tapered opening for filling it to seal the inside of the tube while simultaneously causing the connector element to sink into the ribs on the end of the tube for securing it thereto.

These and other objects of the present invention are attained in one working embodiment by a method that includes rolling a blank of sheet material into a tube having a controlled oval form and seem welding the longitudinal edges along the tube to form one side thereof; thereafter pressing one open end of the tube into a mechanical die of a concave configuration and a particular form that will cause the open end ofthe tube to close on itself into a shape which includes a high density plurality of metal folds defining a tapered small diameter opening in the tube from which a plurality of inwardly and outwardly directed ribs extend to merge into an undeformed portion of the outer surface of the tube. The inwardly and outwardly directed ribs serve to reinforce the end ofthe tube and to define a plurality of spaced apart ledges for supporting a base valve assembly in the shock absorber.

The tapered opening in the tube is closed by heating and pressing metal around the tapered openinginto the opening to close it completely against leakage aoddepressing the connector element simultaneously into the ends of the ribs around the opening therein for connection thereto by means of the melted metal portions of the folds.

The method contemplates a step during the deforming of the open ends of thetube wherein the team weld is located on a part of the concave die at which there is a minimum amount of metal deformation during the formation of an integral cup on the end of the tube.

Furthermore, the method contemplates a coining operation following formation of the tapered opening in the tube wherein the tapered opening through the folded metal at the end of the tube is deformed to produce a controlled diameter opening into the tube not to exceed a predetermined maximum diameter for receiving the melted metal flow during the sealing operation.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred entbodiment of the presentin'vention is clearly shown.

In the drawings:

FIG. I is a view of a sheet metal strip used in the present invention;

FIG. 2 is a vertical sectional view ofa tube formed from the blank and seam welded along the longitudinal edges thereof;

FIG. 3 is a vertical sectional view of the tube of FIG. 2 being aligned with a die;

FIG. 4 is a vertical'eectional view of the tube deformed into the die to form an integral end cup on the tube;

FIG. Sis a vertical sectional view of the parts alter a coining operation;

FIG. 6 is a diagrammatic view showing welding electrodes electrically connected to welding apparatus together with means for pressing a connector into the tube for sealing the tube while securing the connector to the tube;

FIG. 7 is a top elevatlonal view of the die used in the process;

FIG. 8 is a vertical sectional view taken along line 8-8 of FIG. 7 looking in the direction. of the arrows;

FIG. 9 is a side elevational view of the end of a punch used in the coining operation;

FIG. 10 is an enlarged fragmentaryaectional view of the end of the tube following metal formingsteps;

FIG. It is a view partly in elevation and partly in vertical section of a shock absorber having a reservoir tube made in accordance with the present invention;

FIG. 12 is a view in vertical section of the tube and connector prior to weld;

FIG. 13 is a view in horizontal section taken along the line 13-13 ofFlG. "and FIG. 14 is a horizontal sectional view taken along the line [4-14 of FIG. it looking in the direction of the arrows.

Referring now to the drawings. in FIG. I] a hydraulic shock absorber is illustrated having a pressure cylinder 22 closed at the base thereof by a base valve assembly 24 and at the top end thereof by a rod guide 16.

The base valve assembly 24 more particularly includes an orificed valving element 28 with a peripheral flange 30 seated on an annular valve seat 32 around a central opening 34 through the base valve assembly 24 which communicates the interior of the pressure cylinder 22 with a reservoir space 36 formed between the pressure cylinder 22 and a reservoir tube 38.

More particularly, the valving element 28 is held against the seat 32 by a light spring element 40 that regulates the flow from the reservoir 36 into the presure tube 22 during a rebound stroke of the shock absorber.

During a compression stroke the valving element 28 is maintained against the seat 32 and flow control is obtained across a fixed orifice 42 through the valvlng element 28.

The reservoir tube 38 is closed at the top by an inverted cap member 44 which has an end opening 46 therein through which extends a piston rod 48.

The piston rod 48 is connected to the upper end thereof to a closure member 50 connected to the top of a tubular dust shield element 52 located in surrounding telescoping relationship with the outer surface of the reservoir tube 38.

The inverted cup element 44 defines the top of a rod seal assembly 52 which includes an annular resilient multllipped resilient seal member 54 having its upperend in engagement with the under surface of the cup element 44 and the under surface thereof supported by a washer 56 that is engaged by the upper end of a spring element 58 having its opposite end supportingly received within an annular groove 60 in the upper surface of the rod guide 26.

The rod guide further includes a tubular bearing segment 62 thereon that guides the piston rod 48 in axial alignment with the pressure-cylinder 22 during reciprocation of the rod into and out of the cylinder 22.

Damping'during rebound and compression strokes of the shock absorber also is under the control of a piston assembly 64 that includes a base member 66 connected to a small diameter end 68 on the rod 48.

In this arrangement the base 66 defines a top of a control chamber 70 which communicates with a rod flow passageway 72 arranged on the axis of rod 48. it has a side outlet port 74 into a rebound chamber 76 of the pressure cylinder 22.

The rebound chamber 76 is separated from a compression chamber 78 by an annular scaling element 80 on the outside surface of the base member 66 which is supported in sliding sealing engagement with the inner surface of the tube 22.

The base includes an inwardly tun-ted flange 82 thereon which supportingly receives the peripheral flange of a performed sheet metal valve cage 84 which depends downwardly from the piston assembly 64 and has a generally truncated conical configuration.

it supports a rebound valve spring 86 that maintains a rebound valving element 88 against a valve plate 90 within the control chamber 70.

The upper surface of plate 90 supportingly receives a rebound valve element 92 held in place by a spring 94.

The details of the valve assembly 64 form no part of the present invention and are merely representative of a construction found in double direct acting hydraulic shock absorbers and operative to maintain distinct damping characteristics in response to road conditions that cause the piston rod 48 to move into and out of the hydraulic fluid filled pressure cylinder 22.

In shoclt absorbers of this type there is a predetermined level of hydraulic fluid within the reservoir 36 which flows into and out of the pressure cylinder 22 to accommodate changes in the volume within cylinder 22 occupied by the piston rod 48 during its relative reciprocation into and out of cylinder 22. A groove 95 in tube 38 forms a bsffle within the reservoir space 36 to reduce aeration of hydraulic fluid therein.

The upper end of the piston rod 48 is connected to a bearing ring 96 which serves as a means for connecting the upper end of the shock absorber to the sprung mass of a vehicle.

The opposite end of the shock absorber 20 has an improved lightweight. high strength configuration that is formed in accordance with certain principles of the present invention.

More particularly, the bottom end of the reservoir tube 38 is cup formed as an integral part of the tube and u connected to a bottom bearing ring 98 by a method which results in a sealed high strength end configuration suitable for heavy duty use.

It includes a longitudinal seam weld 99 therealong which results in a reservoir tube 38 of a unitary form with an integral cup end which eliminates the need for a separate cylinder base cup and a welded joint between such a base cup and the reservoir tube as found in many present day shock absorbers In addition to eliminating a part and a sealed joint. the improved reservoir tube 38 includes advantageous structural features that reinforce the shock absorber 20 in the vicinity of the base bearing ring 98. These features also locate and support the base valve assembly 24 lnteriorly of the tube 38 to accommodate for unrestricted flow of fluid between reservoir 36 and the interior of the tube 22.

More particularly, the tube 38 at the bottom end thereof includes a plurality of equally circumferentially spaced flutes I00 therein.

Each of the flutes 100 include a distinct configuration that serves to define a reference support for the internal operative components of the shock absorber 20 as well as to reinforce the lower end of the shock absorber unit 20 against high concentrations of stress directed thereto by normal road movement between the sprung and the unsprung mass of the vehicle.

More particularly. each of the flutes 100 include an inwardly located formed ridge or rib 102 which has a bent end defining a flat end surface [04 adjacent a tapered opening 106 which n filled by a plug of sealing material 108.

Each of the ribs or ridges 102 merges into the undeformed side wall of the tube 38 along a peripheral circumference l 10 at a predetermined point along the height of tube 38.

Additionally, each of the flutes 100 includes an outwardly formed ridge or rib surface I12 that is joined at each side thereof by a surface H4, to an adjacent one of the inwardly formed ribs or ridges I02.

The inwardly directed ribs I12 each include an internal surface I16 formed thereon which supportingly receives a con' tinuous circumferential, inclined surface l 18 on the bottom of the base valve 24 for locating it and the end of the pressure cylinder 22 axially within the shock absorber 20.

Furthermore. the support surface 116 is joined to the flat surface 104 through a curved inner surface 120 which serves as a transition between the flat end surface 104 and the base valve supporting surface 116. The outwardly formed surfaces 112 define flow passageways 121 as shown in FIG. l3 for the flow of hydraulic fluid into and out of reservoir 36 during shock operation.

In the illustrated arrangement the outer surface 121 of the bottom bearing ring 98 is slightly depressed into the end of the outer ridges I12 around'the opening 106 therein to be fused in bridging relationship across adjacent ones of the ridges and to plug [08 for fixedly and rigidly securing the bearing ring 98 on the end of the rib reinforced closure on the reservoir tube 48.

with reference to FIGS. 7 and 8 a single female die is illustrated that is used in practicing the process of the present invention.

More particularly, it is the means by which the aforedescribed flute structure is obtained in closing the integral cup end ofthe reservoir tube 38.

The die 122 includes a concave inner surface 124 which has a central opening 126 therethrough.

The concave surface I24 is formed in a generally conoidal configuration above the opening 126. More particularly. it includes a plurality of radially outwardly directed grooves 128 with a maximum depth adjacent the opening 126 and a minimum depth at a point where they merge with the upper periphery 130 of the surface 124.

Each of he grooves I28 is slightly tapered at the point that it intersects an adjacent groove as at 132 in FIG. 7.

The tapered section is defined on the opposite sides thereof by transition edges 134 formed on the surface 124 and curved as shown in FIG. 8 to define a relatively sharp lead edge from opening 126 to a raised surface or ridge 136 between each of the adjacent grooves 128.

As viewed in FIG. 7 each of the ridge surfaces 136 has a triangular configuration with an apex at the upper end of each of the edges 134. They also include a base portion which merges into the generally cylindrical upper inner surface edge I30 of the concave surface 124.

The die I22 constitutes a single processing tool that simultaneously forms the reinforcing flutes I00 and the opening 106 as well as a configuration of folded metal on the tube 38 to be described from which material is heated to flow into the tapered opening I06 to eventually define the weld plug I08.

A further aspect of the present invention is an intermediate process step wherein the diameter of the tapered opening I06 is closed controlled while the base valve supporting surfaces 116 are defined in the inwardly directed ribs 102.

Referring now to FIG. 9, a coin punch 140 is illustrated that includes an end surface 142 thereon including a truncated transition surface I44 that connects a large diameter upper portion I46 ofthe punch to a smaller diameter portion 148.

The end of the smaller diameter portion I48 has a flat end portion 150 which is joined to a curved segment 152 that defines a transition between the flat end surface I50 and the outer periphery of the small diameter portion 148.

As seen in FIG. 9. the punch includes a top head I54 which is acted upon by a hydraulic press to move the end of the coining punch into engagement with the end of formed tube for simultaneously configuring the inner surface thereof in accordance with he shape ofthe end 142.

To assemble a shock absorber reservoir tube in accordance with the invention first a reservoir tube is formed in a tube mill. It is made from a thin gauge material having a thickness in the order of0.0380.046 inches Strip steel of this thickness having a predetermined width is rolled on itself as shown in FIG. 2 to have a maximum oval shape not to exceed 0.008 inches as rolled.

The strip has longitudinal edges I58, 160 thereon that are located in close proximity to one another following rolling and thereafter these edges are joined together by a seam weld 99 as the strip of material passes through the tube mill.

In the mill the I. D. weld bead is rolled to give a smooth surface along the weld and a maximum height through the weld not to exceed 0.0 l0 inches.

This rolled and welded member I62 assumes an elongated tubular shape which has its end 164 fed into a single female die station shown in FIG. 3 wherein a die I22 corresponding to that shown in FIGS. 7 and 8 is supported on a work platform 166 in alignment therewith.

At this station the longitudinal weld seam 99 is located in axial alignment with the die by indexing means, for example a small depth groove I68 formed in the outer surface of the tubular member 162 as it is rolled and an indexing arm 170 upstanding from the work platform I56.

More particularly, the indexing of the arm I70 and the groove I68 locates the longitudinal seam weld 99 in overlying relationship with the portion ofthe concave surface I24 which gives the greatest support to the tubular member or process tube I62 during a metal forming operation to be discussed.

Thus. as illustrated in FIG. 3, the seam weld is in alignment with the transition edge 134 leading into the upper surface I36 which will support the longitudinal weld 99 as the tube 162 is being acted upon by the single female die 122.

In accordance with certain principles of the present invention a hydraulic press acts on the upper end 172 of the process tube 162 to force it into the concave surface 124.

This action causes the end of the tube I62 to be folded and deformed across the inside surface of the die I22.

More particularly. the end I65 has its metal folded radially inwardly and forced into each of the grooves 128 of the concave surface 124 to form each one of the circumferentially spaced inwardly directed ridges 102 from the peripheral inner surface I30 ofthe die to the opening 126 therethroughv Simultaneously. the metal is deformed to flow over each of the surfaces I36 to form a plurality of the outwardly directed ridges or surfaces I12 and the surfaces 114 116 on either side of the raised die surfaces 136.

At the same time the metal at the end I65 of the process tube 162 is folded in an accordion fashion around the opening I06 to form a plurality of folds I74 around a small diameter opening in the end I65 as best seen in FIG 14.

The folds I74 have a plurality of sharp radius transitions I76 on the outer surface of the tube end 165 completely around the opening 106 therethrough.

The folds I74 represent a high density concentration of material which will substantially fill the volume of the opening I06 during a subsequent final closure step in the method.

The deformation of the tube 162 into the die as shown in FIG. 3, also produces a controlled foreshortening of the member until it corresponds to the length of the reservoir tube 38in the final shock absorber assembly.

When the tube has been foreshortened a predetermined distance and deformed into the single female die 122 to result in a structure having the plurality of equidistantly circumferentially spaced flutes and the high density folded material 174 around an end opening 106 the process tube 162 is located at a station shown in FIG. 4, where the coin punch is positioned coaxially of the process tube 162 so as to locate the flat surface against the flat end surfaces 104 on the inward ridges or ribs 102.

This can be done when the formed tube 162 is still in the die 122.

The punch is operated by a hydraulic press to press the inward ridges or ribs into a configuration identical to that of the end I42 thereby to simultaneously coin the formed tube around the opening 106 to control its maximum diameter and to produce a generally tapered opening through the end of the process tube 162 at the juncture of each of the ribs and still further form the metal in that vicinity to a more dense configuration.

Simultaneously, the end 142 will form the inwardly directed ribs to the configuration of the surface I52 to define the base valve assembly support surfaces 116.

From the coining operation the process includes a welding step wherein a connector element is secured to the process tube in overlying relationship to the tapered opening I06 therethrough.

In order to avoid leaks the connector is preferably seamless. While shown as a ring element, other connector elements are contemplated for use in practicing the invention such as stud connector or other means suitable for securing the shock absorber 20 in operative position between the sprung and un sprung mass ofa vehicle.

As shown in FIG. 6, the process tube I62 is supported in a hollow arbor 180. It includes an upstanding electrode I82 therein which has an end 184 thereon configured identically to the end 142 on the coin punch,

This rests on the inner surface of the end of the process tube I62 in the same location as did the coin punch following the coining operation.

It is connected by a conductor I86 to one side of weld apparatus I88 that is connected by a conductor to an electrode 192 in a welding press.

The electrode I92 and electrode 182 are moved together by a hydraulic press within the apparatus to apply a predetermined pressure in the order of 3,000 pounds between the ring and the outer surface ofthe process tube 162.

Simultaneously, a preselected welding current is applied across the electrodes 182, I92 causing the high-density metal in the regions of the folds I74 to flow into the controlled diameter opening I06 to form the seal plug 108 within the opening 106.

Sim ultaneously. the ring sinks into the folded metals as illustrated in FIG. 11 to produce a strong mechanical joint between the ring and the processed tube at this point, The position and form of the parts prior to welding are shown in FIG. 12.

In one working arrangement the processed tube was of a low-carbon steel capable of being welded in a DC resistance welding tube mill.

The steel includes the following properties:

(lUSJIIOQ (130-060 8 0.05% maximum 0.047: maximum Sulphur Phosphorus Mechanical Tensile strength, transverse Yield strength. transverse Hardness R Hardness R,

46.0(J5 I v000 psi. 143,000-318,000 p.s.i.

EXAMPLE l Welder set at 100 percent heat; ring squeezed for 74 cycles followed by 50 weld cycles; 45 hold cycles and 2 off cycles. In this example the primary current is 400 amps. It is desirable that the upslope ofthe current cycle be used; for example start upslope at 40 percent heat and reach 100 percent heat in 9 cycles and continue I00 percent heat for remaining weld cycles. This prevents flash. This causes the ring to sink into the fold metal to gain maximum fatigue strength at the structural joint between the bearing ring and the process tube.

EXAMPLE 2 7 weld cycles at 85 percent heat followed by 40 cycles at 75 percent heat.

EXAMPLE 3 l5 weld cycles at 50 80 percent heat.

These welding schedules are merely representative, it being understood that changes in squeeze, weld, hold and off cycles will be required to weld different shaped connectors to the formed tube and to weld different materials. The important considerations are to get a good seal plug in the tube and a seated. welded relationship between connector and tube to assure a good strong joint suitable for stress levels present in automotive shock absorber environments.

in evaluating the resultant structural connection between the bearing ring and the process tube the unit is subjected to fatigue tests wherein it is loaded perpendicular to the centerline of the ring and subjected to a cyclic moment at the opposite end of the shock absorber of 500 inch pounds at 1,625 plus or minus 25 cycles per minute.

The unit was then cycled to failure.

With units welded as set forth in the examples above the fluted tubes averaged from 25,000 to 50,000 cycles before failure.

This compared with standard production shock absorbers wherein a bearing ring is connected directly to a separate base cup element by weld material which failed following between l2,000 and 15,000 cycles.

Additionally, it was noted that in a tensile test wherein the opposite ends or bearing rings 96, 98 of the unit were connected to a tensile machine that the tensile strength of the welded connection between the ring and the fluted end of the process tube were in the order of 9,000 to 10,000 pounds and that in many cases the piston was pulled from the piston rod before the welded connection between the fluted tube and the bottom bearing ring occurred.

From the above data it is clear that in addition to simplifying the manufacture of shock absorber reservoir tubes that the improved method set forth above gives an unusually high strength connection superior to those found in standard production shock absorbers.

While the embodiments of the present invention. as herein disclosed, constitute a preferred form. it is to be understood that other forms might be adopted.

lclaim:

percent heat followed by 25 cycles at l. A method for forming a shock absorber tube having an integral end cup thereon comprising the steps of forming a thin wall metal tube having open ends thereon, forming a concave die surface having a central opening therein and a plurality of grooves extending radially and upwardly of said central opening, forcing one end of the tube into the die to simultaneously reduce the diameter ofthe tube while folding it over the die surface into the grooves and over ribs between the grooves and to crimp the end ofthe tube into a predetermined small diameter high metal density portion with a tapered opening therethrough and sharp edges therearound, coining the end of the tube formed by the die in the vicinity of the tapered opening therethrough to produce a controlled maximum diameter in the opening, locating a connector element in overlying relationship with the opening at the outer surface of the formed tube in contact with the coined end surrounding the opening. applying pressure and welding current across the junction between the formed tube and the connector element to cause the high-density material around the opening to melt and deform into the tapered opening into the tube. maintaining the pressure to cause the connector to sink into the highdensity material for connection thereto and to force it into the opening to completely fill the opening with a plug of melted metal for sealing the formed end of the tube, thereafter removing the heat and pressure and cooling the tube to produce a strong connection between the connector and the tube at the sealed opening.

2. A method for forming a shock absorber tube having an integral cup on one end thereof comprising the steps of; forming a sheet metal tube having a longitudinal seam weld along the length thereof, forming a concave die surface having a central opening therethrough with a plurality of grooves extending from the opening to the top edge of the concave surface separated by raised ribs. circumferentially locating the seam weld along the length of the tube in alignment with a rib on the die between two of the grooves, pressing the tube into the die to form the end of the tube to a smaller diameter by folding metal on the forced end of the tube into the grooves and over the ribs between the grooves to form a plurality of spaced inwardly directed ribs within the tube joined to a plurality of outwardly directed ribs thereon, maintaining the iongitudinal seam weld on the outer surface ofone of the ribs during the forming process to control the amount of metal stretch in the vicinity of the seam weld minimize the probability of leak holes being formed during folding of the metal within the die, forming a high-density crimped annular segment in the folded metal at the die opening to form a tapered opening in the formed end of the tube. coining the formed tube at the tapered opening therethrough to produce a controlled diameter opening into the interior of the tube, locating a connector element on the outer surface of the tube to cover the tapered opening on the outer end surface thereof, simultaneously pressing the connector element against the end surface of the tube and applying welding current thereto for causing the high density material around the opening in the formed end of the tube to flow into the controlled diameter of the opening for filling it with weld metal while securely fastening the connector to the end of the formed tube.

3. A method for manufacturing a shock absorber cylinder having an integral end cup comprising the steps of: forming a blank sheet metal material. rolling said blank into a tubular member, locating adjacent edges of said tubular member in longitudinal alignment with one another, welding said edges together along the length of said tubular member to produce a sealed longitudinal joint along the length of said tubular member, forming a concave die surface having a central opening therethrough and a plurality of radially extending equally spaced grooves extending from said opening to the upper periphery of the die surface, locating one end of said tubular member against the die surface and forcing the one end into the die surface to cause the sheet metal material to be die formed over ridges formed between each of the grooves of the die so as to form a plurality of ribs directed inwardly of the tu bular member, also forming the one end into the grooves of the die to form a plurality of ribs directed outwardly of the tubular member, said ridges and grooves along with the die opening forming a tapered opening through the drawn end of the tubular member and a continuously crimped high-density metal area around the opening through said die having a plurality of sharp edges thereon at the smallest diameter portion of the drawn metal, coining the drawn end of the tube to flatten the high-density material around the opening therein to produce a predetermined maximum diameter at the tapered opening, locating a continuously formed connector element on the outer surface of the formed end in overlying relationship with the coined end of the high density material to close the tapered opening. connecting a first electrode at the controlled diameter of the tapered opening within the interior of the tubular member, connecting a second electrode to the connector element, applying pressure between the connector member and the formed shell and applying welding current across the electrodes to cause the high density material around the tapered opening to become plastic and flow inwardly of the tubular member into the tapered opening, maintaining the pressure to cause the connector element to force the heated plastic material into the tapered opening to fill it so as to completely seal the opening at the controlled diameter portion thereof, and simultaneously forcing the connector element into the end of the tubular member to cause the connector element to bridge between the spaced outwardly directed ribs and be connected thereto by the melted plastic material to securely attach the connector element in place on the end of the tubular member.

4. A method for manufacturing a shock absorber cylinder having an integral end cup comprising the steps of: forming a blank of sheet metal material having a thickness less than approximately 0.050 inches, rolling said blank into a tubular member having a maximum oval shape of less than 0.008 inches, locating adjacent edges of said tubular member in iongitudinal alignment with one another, welding said edges together along the length of said tubular member to produce a sealed longitudinal joint along the length of said tubular member, forming a concave die surface having a central opening therethrough and a plurality of radially extending equally spaced grooves extending from said opening to the upper periphery of the die surface, locating one end of said tubular member against the die surface and forcing the one end into the die surface to cause the sheet metal material to be die formed over ridges formed between each of the grooves of the die so as to form a plurality of ribs directed inwardly ofthe tubular member, also forming the one end into the grooves of the die to form a plurality of ribs directed outwardly of the tubular member, said die ridges and grooves along with the die opening forming a tapered opening through the drawn end of the tubular member and a continuously crimped high-density metai area round the opening through said die having a plurality of sharp edges thereon at the smallest diameter portion of the drawn metal, coining the drawn end of the tube to flatten the high density material around the opening therein to produce a predetermined maximum diameter at the tapered opening, locating a continuously formed connector element on the outer surface of the formed end in overlying relationship with the coined end of the high-density material to close the tapered opening, connecting a first electrode at the controlled diameter of the tapered opening within the interior of the tubular member, connecting a second electrode to the connector element, applying approximately 3,000 pounds of pressure between the connector member and the formed tubular member and applying welding current in the range of 209-400 primary amps for a first controlled number of cycles followed by a second controlled number of cycles to cause the high-density material around the tapered opening to become plastic and flow inwardly of the tubular member into the tapered opening, maintaining the pressure to cause the connector element to force the heated plastic material into the tapered opening to fill it so as to completely seal the opening at the controlled diameter portion thereof, and simultaneously forcing the connector element into the end of the tubular member to cause the connector element to bridge between the spaced outwardly directed ribs and be connected thereto by the melted plastic material to securely attach the connector element in place on the end ofthe tubular member. 

1. A method for forming a shock absorber tube having an integral end cup thereon comprising the steps of forming a thin wall metal tube having open ends thereon, forming a concave die surface having a central opening therein and a plurality of grooves extending radially and upwardly of said central opening, forcing one end of the tube into the die to simultaneously reduce the diameter of the tube while folding it over the die surface into the grooves and over ribs between the grooves and to crimp the end of the tube into a predetermined small diameter high metal density portion with a tapered opening therethrough and sharp edges therearound, coining the end of the tube formed by the die in the vicinity of the tapered opening therethrough to produce a controlled maximum diameter in the opening, locating a connector element in overlying relationship with the opening at the outer surface of the formed tube in contact with the coined end surrounding the opening, applying pressure and welding current across the junction between the formed tube and the connector element to cause the high-density material around the opening to melt and deform into the tapered opening into the tube, maintaining the pressure to cause the connector to sink into the high-density material for connection thereto and to force it into the opening to completely fill the opening with a plug of melted metal for sealing the formed end of the tube, thereafter removing the heat and pressure and cooling the tube to produce a strong connection between the connector and the tube at the sealed opening.
 2. A method for forming a shock absorber tube having an integral cup on one end thereof comprising the steps of; forming a sheet metal tube having a longitudinal seam weld along the length thereof, forming a concave die surface having a central opening therethrough with a plurality of grooves extending from the opening to the top edge of the concave surface separated by raised ribs, circumferentially locating the seam weld along the length of the tube in alignment with a rib on the die between two of the grooves, pressing the tube into the die to form the end of the tube to a smaller diameter by folding metal on the forced end of the tube into the grooves and over the ribs between the grooves to foRm a plurality of spaced inwardly directed ribs within the tube joined to a plurality of outwardly directed ribs thereon, maintaining the longitudinal seam weld on the outer surface of one of the ribs during the forming process to control the amount of metal stretch in the vicinity of the seam weld minimize the probability of leak holes being formed during folding of the metal within the die, forming a high-density crimped annular segment in the folded metal at the die opening to form a tapered opening in the formed end of the tube, coining the formed tube at the tapered opening therethrough to produce a controlled diameter opening into the interior of the tube, locating a connector element on the outer surface of the tube to cover the tapered opening on the outer end surface thereof, simultaneously pressing the connector element against the end surface of the tube and applying welding current thereto for causing the high density material around the opening in the formed end of the tube to flow into the controlled diameter of the opening for filling it with weld metal while securely fastening the connector to the end of the formed tube.
 3. A method for manufacturing a shock absorber cylinder having an integral end cup comprising the steps of: forming a blank sheet metal material, rolling said blank into a tubular member, locating adjacent edges of said tubular member in longitudinal alignment with one another, welding said edges together along the length of said tubular member to produce a sealed longitudinal joint along the length of said tubular member, forming a concave die surface having a central opening therethrough and a plurality of radially extending equally spaced grooves extending from said opening to the upper periphery of the die surface, locating one end of said tubular member against the die surface and forcing the one end into the die surface to cause the sheet metal material to be die formed over ridges formed between each of the grooves of the die so as to form a plurality of ribs directed inwardly of the tubular member, also forming the one end into the grooves of the die to form a plurality of ribs directed outwardly of the tubular member, said ridges and grooves along with the die opening forming a tapered opening through the drawn end of the tubular member and a continuously crimped high-density metal area around the opening through said die having a plurality of sharp edges thereon at the smallest diameter portion of the drawn metal, coining the drawn end of the tube to flatten the high-density material around the opening therein to produce a predetermined maximum diameter at the tapered opening, locating a continuously formed connector element on the outer surface of the formed end in overlying relationship with the coined end of the high density material to close the tapered opening, connecting a first electrode at the controlled diameter of the tapered opening within the interior of the tubular member, connecting a second electrode to the connector element, applying pressure between the connector member and the formed shell and applying welding current across the electrodes to cause the high density material around the tapered opening to become plastic and flow inwardly of the tubular member into the tapered opening, maintaining the pressure to cause the connector element to force the heated plastic material into the tapered opening to fill it so as to completely seal the opening at the controlled diameter portion thereof, and simultaneously forcing the connector element into the end of the tubular member to cause the connector element to bridge between the spaced outwardly directed ribs and be connected thereto by the melted plastic material to securely attach the connector element in place on the end of the tubular member.
 4. A method for manufacturing a shock absorber cylinder having an integral end cup comprising the steps of: forming a blank of sheet metal material having a thickness less than approximately 0.050 inches, rolling saiD blank into a tubular member having a maximum oval shape of less than 0.008 inches, locating adjacent edges of said tubular member in longitudinal alignment with one another, welding said edges together along the length of said tubular member to produce a sealed longitudinal joint along the length of said tubular member, forming a concave die surface having a central opening therethrough and a plurality of radially extending equally spaced grooves extending from said opening to the upper periphery of the die surface, locating one end of said tubular member against the die surface and forcing the one end into the die surface to cause the sheet metal material to be die formed over ridges formed between each of the grooves of the die so as to form a plurality of ribs directed inwardly of the tubular member, also forming the one end into the grooves of the die to form a plurality of ribs directed outwardly of the tubular member, said die ridges and grooves along with the die opening forming a tapered opening through the drawn end of the tubular member and a continuously crimped high-density metal area round the opening through said die having a plurality of sharp edges thereon at the smallest diameter portion of the drawn metal, coining the drawn end of the tube to flatten the high density material around the opening therein to produce a predetermined maximum diameter at the tapered opening, locating a continuously formed connector element on the outer surface of the formed end in overlying relationship with the coined end of the high-density material to close the tapered opening, connecting a first electrode at the controlled diameter of the tapered opening within the interior of the tubular member, connecting a second electrode to the connector element, applying approximately 3,000 pounds of pressure between the connector member and the formed tubular member and applying welding current in the range of 200-400 primary amps for a first controlled number of cycles followed by a second controlled number of cycles to cause the high-density material around the tapered opening to become plastic and flow inwardly of the tubular member into the tapered opening, maintaining the pressure to cause the connector element to force the heated plastic material into the tapered opening to fill it so as to completely seal the opening at the controlled diameter portion thereof, and simultaneously forcing the connector element into the end of the tubular member to cause the connector element to bridge between the spaced outwardly directed ribs and be connected thereto by the melted plastic material to securely attach the connector element in place on the end of the tubular member. 